Driving under the influence of marijuana is not as dangerous as drunk, but there are risks.

I know all about the dangers of drunk driving. But is driving under the influence of marijuana just as dangerous?

Driving under the influence of any intoxicant is obviously a bad idea, but smoking a joint or ingesting a edible before getting behind the wheel can pose different risks. This, experts say, is because of the specific ways marijuana affects the brain and the fact that there is no standard dose for a drug criminalized by the federal government.

When it comes to alcohol, there are universally accepted amounts for what constitutes a single drink: 340 ml of regular beer, 142 ml of wine and 42.6 ml of spirits. There is no agreed-upon equivalent for cannabis, said Marlene Lira, senior research manager at the Clinical Addiction Research and Education Unit at Boston Medical Center in the United States. This makes it difficult for consumers to measure how much they actually used.

Over the past decade, car accidents involving cannabis have increased, and recreational use of the drug continues to grow. A recent analysis of US public safety data showed that from 2000 to 2018, the percentage of motor vehicle deaths involving marijuana more than doubled, from 9% to about 22%. On the other hand, the percentage of deaths involving alcohol remained practically the same.

While there is a paucity of data directly comparing the dangers of high versus drunk driving, existing research suggests that marijuana may be less likely than alcohol to lead to deadly car accidents.

In a 2017 assessment of more than 4,000 drivers from a French police database, researchers found that drivers under the influence of alcohol were approximately 17.8 times more likely to be responsible for car accidents. car fatalities than sober drivers, while drivers under the influence of marijuana were 1.65 times more likely to cause fatal accidents.

Studies like these often rely on drivers who have passed drug tests after car accidents. But since marijuana can remain in fatty tissues for up to 28 days, a positive drug test does not necessarily mean that a driver was using the drug at the time he was driving.

It is also tricky for marijuana users to predict exactly how they will be harmed and for how long. If you smoke a joint or a pipe, you’ll feel high in minutes and then go back to the basic level after three or four hours, said Dr. Godfrey Pearlson, a professor of neuroscience at Yale University who has researched marijuana and car safety. Whether you opt for a marijuana brownie or a gummy bear, it takes longer for the effect to kick in, as the marijuana in edibles needs to be absorbed by the intestines and metabolized by the liver.

“If someone uses an edible, the classic scenario is to say, ‘Hey, I’m not feeling anything,’ and after 40 minutes they get in a car and start driving,” said Dr. Collin Reiff, a psychiatrist at Langone Health at New York University.

THC (tetrahydrocannabinol), the intoxicating substance in cannabis, impairs several driving-related behaviors, including the ability to switch between traffic lanes. It also slows down response times in general, Lira said.

The psychoactive effects of marijuana can also make driving dangerous. The paranoia some people feel while high can induce a panic attack while on the road, Reiff said. The herb can also create an altered sense of time, the feeling that everything around you is moving slower than it actually is.

“There’s that joke: why were you stopped?” he said. “If you’re speeding too fast, it’s because of the alcohol. If you’re going too slow, it’s because of the weed.”

Translated by Luiz Roberto M. Gonçalves